1. Field of the Invention
The present invention relates to an optical pointing device and a power supply semiconductor device therefor.
2. Description of Related Art
In general, an optical pointing device includes an optical unit, an image sensor, a motion value calculator, and an analog-to-digital (A/D) converter. Since a semiconductor device used for the optical pointing device is a system-on-chip (SOC), optimum operating voltages required for internal blocks are all different. Specifically, the operating voltage of the optical unit must be a threshold voltage or higher (here, the threshold voltage of a red light emitting diode (LED) is 2.7V, and the threshold voltage of a blue LED is 3.2V). The image sensor operates at a high voltage so that a depletion region is increased to elevate optical efficiency. A logic unit, such as a motion value calculator, may operate at a comparatively lower voltage, and the operating voltage of the A/D converter is intermediate between the operating voltage of the image sensor and the operating voltage of the logic unit, so that the A/D converter can operate at both operating voltages of the image sensor and the logic units.
Meanwhile, since a radio-frequency (RF) signal output from a semiconductor device for a wireless optical pointing device is basically dependent on a power supply voltage, it may be necessary for the RF circuit block to be adaptable for various operating voltage at user's request. Also, a portable battery is typically used for a wireless optical pointing device as a power source and thus, a recent increase in popularity of low-power portable electronic appliances has led to a strong need for complementing the power supply management of the semiconductor device.
Similarly, with rapid developments in semiconductor micro-processing technology, the power supply voltage of a semiconductor device used for a wired optical pointing device is dropping in order to endure the maximum permitted internal voltage. Also, in order to meet the required specifications of high-speed systems, such as high-speed digital communication systems, high-resolution high-speed display devices, and high-capacity storage devices, analog and digital blocks included in the high-speed systems are showing a tendency to employ a plurality of power supply voltages.
Therefore, when some semiconductor devices or some internal circuits of semiconductor devices require high operating voltages due to their operational characteristics, voltage management is needed.
FIG. 1 is a block diagram of a conventional optical pointing device.
Referring to FIG. 1, the conventional optical pointing device includes an optical unit 40, a motion sensor 50, a microcontroller 60, a wireless data transceiver 70, and a power supply 20. The motion sensor 50 includes an image sensor 51, an A/D converter 52, and a motion value calculator 53.
Functions of the respective blocks shown in FIG. 1 will now be described.
The optical unit 40 includes a light source, a lens, and other attachments. Light irradiated by the light source is reflected by an object and incident to the image sensor 51 through the lens.
The motion sensor 50 receives an optical image with the optical unit 40 and calculates a motion value V(MOV) using the optical image. The image sensor 51 receives the reflected light through the lens and senses image data. The A/D converter 52 receives an analog signal from the image sensor 51 and converts the analog signal into a digital signal. The motion value calculator 53 calculates the motion value V(MOV) based on the image data, which is an output signal of the A/D converter 52, and outputs the motion value V(MOV).
The microcontroller 60 receives not only the motion value V(MOV) output from the motion sensor 50 but also other external input information, such as a button input value and a scroll input value of the optical pointing device, and transmits the motion value V(MOV) and the external input information to a host computer (not shown) according to specifications required by the host computer.
When the optical pointing device is a wireless device, the wireless data transceiver 70 is further prepared at a rear end of the microcontroller 60. The wireless data transceiver 70 wirelessly receives the request to transmit the motion data of the optical pointing device through an antenna 80 from the host computer, receives the motion value from the microcontroller 60, converts the motion value into an analog signal, and wirelessly transmits the analog signal through the antenna 80 to the host computer.
The power supply 20 applies a fixed power supply voltage V_fix required for all the internal blocks of the optical pointing device to perform respective functions.
Operation of the conventional optical pointing device will now be described with reference to FIG. 1.
When the optical unit 40 irradiates light to an object using the light source and the light reflected by the object is incident on the image sensor 51 through the lens, the image sensor 51 receives the light, senses image data of the object, and outputs a photovoltage (or a photocurrent) corresponding to the amount of the received light.
The A/D converter 52 receives an analog signal of the photovoltage (or the photocurrent) output from the image sensor 51, converts the analog signal into a digital signal, and outputs the digital signal. The motion value calculator 53 receives image data, which is the output signal of the A/D converter 52, calculates a motion value V(MOV) of the optical mouse, and outputs the motion value V(MOV).
The power supply 20 applies a fixed power supply voltage V_fix required for the internal blocks of the optical pointing device, namely, the optical unit 40, the motion sensor 50, the microcontroller 60, and the wireless data transceiver 70, to perform the functions.
In this case, the optical pointing device, which moves on an arbitrary surface, should obtain discontinuous image frames and compare and analyze the image frames in order to calculate a motion value. Therefore, the operating speed of circuits, for example, a rate of obtaining image frames, should catch up with the operating speed of the optical pointing device so that the optical pointing device can obtain a proper motion value.
As described above, even if the conventional optical pointing device operates at the highest speed, a fixed power supply voltage corresponding to the highest operating speed is applied to the internal circuits thereof not to give rise to any problem.
FIG. 2 is a block diagram of the power supply of the conventional optical pointing device shown in FIG. 1.
Referring to FIG. 2, the power supply 20 includes a power source 10 and a direct current (DC)-to-DC converter 15.
Functions of the respective blocks shown in FIG. 2 will now be described.
The power source 10 applies a predetermined level of power supply voltage, and the DC-to-DC converter 15 receives the power supply voltage, boosts the power supply voltage to the highest voltage required as an operating voltage by an internal block, and outputs the highest voltage to a plurality of internal blocks (not shown).
The internal blocks receive the highest voltage from the DC-to-DC converter 15 and perform respective functions using the highest voltage as the operating voltage.
As a result, some internal blocks, which may operate at the minimum voltage, receive an excessively high operating voltage to cause waste of power. For example, a current consumed by a CMOS logic circuit is determined by the product of a power supply voltage, a capacitance, and an operating frequency. Therefore, an excessively high operating voltage applied to the CMOS logic circuit leads to a rise in current consumption, thus resulting in inefficiency and waste of power.
In order to solve these problems, a method of employing a portable power source has been conventionally proposed. Specifically, a low voltage may be applied from the portable power source to specific ones of the internal blocks, while a high voltage may be applied from a predetermined constant voltage generator to the remaining blocks. For example, a battery power supply voltage of 1.5V may be applied from a portable battery to a logic unit of an optical pointing device, which can operate normally at a low voltage, while the battery power supply voltage may be boosted to a constant voltage of 3.0V or higher using a DC-to-DC converter and the boosted voltage may be applied to a light source, an image sensor, and an A/D converter of the optical pointing device.
In this method, however, repeated use over a long period of the portable battery leads to a drop in an output voltage of the portable battery. Thus, a reduced power supply voltage is applied to the logic unit, while a constant boosted voltage is applied to the other blocks. As a result, logic circuit design is subject to restrictions in power consumption.